x = 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 .
x = 2 + 4 + 6 + 8 + 10 + 12 + 14 + 16 + 18 + 20 .
x = 1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19 .
Nếu: 7 + 7 = 2
8 + 8 = 4
8 + 5 = 1
6 + 9 = 3
10 + 11 = 9
Thì: 4 + 9 = ?
1+2+3+4+5+6+7+8+9+10+11=?
11 10 9 8 7 6 5 4 3 2 1=0
Tính: 1+2-3+4-5+6-7+8-9+10-11+12-13+14-15+16-17+18-19+20 = ?
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20-1-5-9-3=
\(1+2+3+4+5+6+7+8+9+10+11=???\)
1+2+3+4+5+6+7+8+9+10+11=..........
( Tình nhanh nha)
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+................+200